Lysine is an essential amino acid, one that you need to get from food. Some evidence suggests that supplemental lysine may be able to help prevent herpes infections (cold sores and genital herpes).

Requirements/Sources

Most people need about 1 g of lysine per day. The requirement may be greater for athletes and people recovering from major injuries, especially burns. The richest sources of lysine are animal proteins such as meat and poultry, but it is also found in dairy products, eggs, and beans.

Therapeutic Dosages

A typical therapeutic dosage of lysine for
herpes infections
is 1 g three times daily. You can take this as a regular part of your diet in hopes of preventing herpes flare-ups, or, perhaps, at the first sign of an attack. Although the evidence isn't strong, there may be some advantage to restricting your intake of foods that contain a lot of arginine, such as chocolate, peanuts, other nuts and seeds, and, to a lesser extent, wheat.

Therapeutic Uses

Some small studies suggest that
regular
use of lysine supplements can help prevent flare-ups of cold sores and genital herpes, although other studies have not found benefit.
1-6,18,19
Lysine has also been proposed as a treatment to take at the
onset
of a flare-up, but at least one study failed to find it effective for this purpose.
7

Both cold sores and genital herpes are caused by a virus called
herpes simplex
.
After you are first infected, this virus hides in certain nerve cells and reemerges under times of
stress
. Test tube research suggests that lysine fights this virus by blocking
arginine
, an amino acid the virus needs in order to replicate.
8
For this reason, lysine might be most effective when used in conjunction with a low-arginine diet. However, this widely stated claim has not been proven. (Note that if this is true, it would be essential to avoid taking arginine supplements if you have herpes.)

What Is the Scientific Evidence for Lysine?

When taken in sufficient doses, it appears that regular use of lysine supplements might be able to reduce the number and intensity of herpes flare-ups.
9

One
double-blind, placebo-controlled study
followed 52 participants with a history of herpes flare-ups.
11
While receiving 3 g of L-lysine every day for 6 months, the treatment group experienced an average of 2.4 fewer herpes flare-ups than the placebo group—a significant difference. The lysine group's flare-ups were also significantly less severe and healed faster.

Another double-blind placebo-controlled crossover study on 41 subjects also found improvements in the frequency of attacks.
12
Interestingly, this study found that 1,250 mg of lysine daily worked, but 624 mg did not.

Other studies, including one that followed 65 individuals, found no benefit, but they used lower dosages of lysine.
13,14

Although some are promising, none of these studies are large enough to give conclusive answers. At this point, more evidence is needed to determine whether lysine is effective for preventing herpes simplex.

Many people use lysine in a different way—they take it at the onset of a herpes attack. However, a double-blind, placebo-controlled study evaluating this method found no benefit.
10
(Consider using the herb
lemon balm
instead.)

Safety Issues

Although lysine is an essential part of the diet, the safety of concentrated lysine supplements has not been well studied. In animal studies, high dosages have caused gallstones and elevated cholesterol levels,
15,16
so you may want to use caution when using lysine if you have either of these problems. Maximum safe dosages for young children, pregnant or nursing women, or those with severe liver or kidney disease have not been established.

Interactions You Should Know About

If you are taking lysine to treat herpes,
arginine
might counteract the potential benefit.
17

Revision Information

This content is reviewed regularly and is updated when new and relevant evidence is made available. This information is neither intended nor implied to be a substitute for professional medical advice. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with questions regarding a medical condition.